A number of research systems have demonstrated the benefits of
accompanying each request with a machine-checkable proof that the
request complies with access-control policy --- a technique called
proof-carrying authorization. Numerous authorization logics have been
proposed as vehicles by which these proofs can be expressed and
checked. A challenge in building such systems is how to allow
delegation between institutions that use different authorization
logics. Instead of trying to develop the authorization logic that all
institutions should use, we propose a framework for interfacing
different, mutually incompatible authorization logics. Our framework
provides a very small set of primitives that defines an interface for
communication between different logics without imposing any
fundamental constraints on their design or nature. We illustrate by
example that a variety of different logics can communicate over this
interface, and show formally that supporting the interface does not
impinge on the integrity of each individual logic. We also describe an
architecture for constructing authorization proofs that contain
components from different logics and report on the performance of a
prototype proof checker.